How to pre-define symbols?

[frozax]

I'm using vscode and python for https://py.processing.org/.
In this environnement, some symbols are available without being imported. For example, frameRate and circle are valid methods, and frameCount and width are variables.
How could I give a list of those symbols (eventually with a prototype for function) to Pylance to avoid reportUndefinedVariable?

Thanks for your help!

[erictraut]

While Python allows code to "insert" symbols into the namespace of another module, this practice is very fragile, and I would highly discourage library authors from using it. It potentially overwrites symbols of the same name in other modules, and it makes code difficult to follow (both for static code tools and for humans). Symbols should be imported explicitly to avoid namespace collisions.

If you are the consumer of a library that implements this dangerous and ill-advised behavior, you have a few options:

1. Although the symbol is already implicitly "inserted" into your module's namespace, use a proper explicit import statement to import the symbol again. Pylance and other tools (and readers of your code) will then be aware of where that symbol originates and how it came to be part of your module's namespace.

from processing import frameRate, frameCount

2. Conditionally define the types of these symbols within a TYPE_CHECKING block within your module:

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    def frameRate(a: int, b: str) -> int: ...
    frameCount: int

The first of these two options is preferable if it works.

[frozax]

Thanks Eric for the reply.

There is actually no processing stuff to import. Everything is hidden with a specific interpreter (yes, it's a bit hacky: https://py.processing.org/tutorials/python-jython-java/). If I create a fake module with a frameCount and import it in my code for example, it override the actual one.

I basically would like to tell pylance: "here is a list of valid symbols, believe me" ;)

Also, I'm not sure to understand your 2nd solution?

[erictraut]

Oh, that's really hacky. Yikes!!!

You can create a fake module and import it under the TYPE_CHECKING hint. That way, it won't execute at runtime but static type checkers like Pylance will make use of it during static analysis.

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    # Provide types for symbols that are auto-imported by "processing"
    from _processing import frameRate, frameCount

You can define the symbols in a type stub file located in the root of your project.

# _processing.pyi

def frameRate(a: int, b: str) -> int: ...
frameCount: int
# etc.